Evanko S P, Vogel K G
Department of Biology, University of New Mexico, Albuquerque 87131.
Arch Biochem Biophys. 1993 Nov 15;307(1):153-64. doi: 10.1006/abbi.1993.1574.
The predominant proteoglycan in tensional regions of tendon is the small proteoglycan decorin. However, a fibrocartilaginous tissue containing large amounts of aggrecan and biglycan develops at points where tendon wraps under bone and is subjected to compressive loading in addition to tension. The hypothesis that local compression regulates the development of fibrocartilage in tendon was tested by assessing the effect of in vitro compressive loading on proteoglycan synthesis. Fetal bovine deep flexor tendon explants from the region which would have become fibrocartilage were subjected to 3 days of continuous cyclic uniaxial compression (unconfined) to 30% strain, at a frequency of 1 cycle/6 s (0.17 Hz). Compression was perpendicular to the long axis of the tendon. Large proteoglycan, biglycan, and decorin were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and [35S]sulfate incorporated into each proteoglycan was quantitated by liquid scintillation counting of gel slices. The primary effect of compression was to stimulate selectively synthesis of large proteoglycan and biglycan. Incorporation of [35S]sulfate into large proteoglycan was increased 100-300% and incorporation into biglycan was increased 50-150% in compressed tissue compared to matched uncompressed tissue segments. Incorporation into decorin was unchanged. A similar effect on radio-sulfate incorporation was seen following loading of tissue from the tensional region of tendon, which does not normally develop into fibrocartilage. Proteoglycans from compressed tissue were larger, due to slightly longer glycosaminoglycan chains. Disaccharide analysis showed that the C6S/C4S ratio was higher in both the large and the small proteoglycan populations from compressed tissue. Aggrecan mRNA levels were increased approximately fivefold in loaded tissue, and SDS-PAGE analysis of [3H]leucine-labeled core proteins indicated that large proteoglycan core protein synthesis was increased by compression. The selective changes in large proteoglycan and biglycan synthesis, and in the sulfate composition and size of the glycosminoglycan chains, are consistent with what might be expected during development of fibrocartilage in vivo. These observations support the hypothesis that compressive force can regulate the development of fibrocartilaginous tissue in tendon.
肌腱张力区域中占主导地位的蛋白聚糖是小分子蛋白聚糖核心蛋白聚糖。然而，在肌腱环绕骨骼的部位会形成一种含有大量聚集蛋白聚糖和双糖链蛋白聚糖的纤维软骨组织，该部位除了承受张力外还会受到压缩载荷。通过评估体外压缩载荷对蛋白聚糖合成的影响，对局部压缩调节肌腱中纤维软骨发育的假说进行了验证。取自可能会形成纤维软骨区域的胎牛深屈肌腱外植体，在3天的时间里，以1个周期/6秒（0.17赫兹）的频率，持续进行单轴循环无侧限压缩至30%应变。压缩方向垂直于肌腱的长轴。通过十二烷基硫酸钠-聚丙烯酰胺凝胶电泳（SDS-PAGE）分离大分子蛋白聚糖、双糖链蛋白聚糖和核心蛋白聚糖，并通过对凝胶切片进行液体闪烁计数来定量掺入每种蛋白聚糖中的[35S]硫酸盐。压缩的主要作用是选择性地刺激大分子蛋白聚糖和双糖链蛋白聚糖的合成。与匹配的未压缩组织片段相比，压缩组织中[35S]硫酸盐掺入大分子蛋白聚糖增加了100 - 300%，掺入双糖链蛋白聚糖增加了50 - 150%。掺入核心蛋白聚糖的量没有变化。对来自肌腱张力区域（通常不会发育成纤维软骨）的组织加载后，也观察到了对放射性硫酸盐掺入的类似影响。由于糖胺聚糖链略长，压缩组织中的蛋白聚糖更大。二糖分析表明，压缩组织中大分子和小分子蛋白聚糖群体的C6S/C4S比值更高。加载组织中聚集蛋白聚糖mRNA水平增加了约五倍，对[3H]亮氨酸标记的核心蛋白进行SDS-PAGE分析表明，压缩增加了大分子蛋白聚糖核心蛋白的合成。大分子蛋白聚糖和双糖链蛋白聚糖合成的选择性变化，以及糖胺聚糖链的硫酸盐组成和大小的变化，与体内纤维软骨发育过程中预期的情况一致。这些观察结果支持了压缩力可调节肌腱中纤维软骨组织发育的假说。
